1. Field of the Invention
The present invention relates to an apparatus and method to produce steam, gas, and solid waste without waste water from low quality water and low quality fuel by direct contact in a rotating pressurized vessel.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Generally, steam production facilities are divided into two main types: direct contact steam production facilities, and indirect steam facilities steam production facilities. In direct contact steam production facilities, water is mixed with hot gases to produce steam by direct heat exchange between the water and the gases to provide a mixture of steam and gas. In an indirect steam production facility, the heat that is required to produce the steam from the water is provided through a metal wall, typically a steel wall, that prevents the mixture of the water and hot gases.
Indirect contact steam generation is widely used for steam production. The devices vary from steam drum boilers to Once-Through Steam Generators (OTSG). The heat exchange can be by radiation, convection or both.
The direct-contact steam generators are much more limited in use than the non-direct contact steam generator. One of the proven applications for the direct contact steam generation process is enhanced oil recovery (EOR), wherein steam and flue gas (mainly CO2) mixtures are injected into a heavy oil reservoir to increase oil mobilization in heavy oil production.
The main characteristic of the direct contact steam generator is that the produced steam contains impurities, such as combustion products (mainly gases and possible solids) that were burned during production of the steam. Those gases are mainly carbon dioxide and nitrogen, when air is used for the combustion process. Additional gases can be present in smaller percentage such as CO, SOx, NOx and other gases. Due to the presence of combustion gases, the steam produced by direct contact will be used in open circuit systems or in systems that can handle the impurities in the steam.
In recent years, the advantages of direct contact steam generators have become more obvious due to increased awareness of the need to reduce greenhouse gas emissions. Direct contact steam generators are devices preventing such greenhouse gas emissions, for example, by injecting CO2. In the example of the direct contact steam generator for heavy oil recovery applications, portions of injected harmful CO2 gas will permanently stay underground and will not be released into the atmosphere.
The need for the present invention is driven by the challenges facing the heavy oil production industry involved with enhanced oil recovery (EOR), and in particular, steam assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS). The disadvantages of the prior art in direct steam generation prevented SAGD and CSS from becoming preferred commercial solutions for EOR. As a result, indirect steam generator, mainly OTSG and steam drums, are used commercially as the alternative. In the prior art, the systems of both direct and indirect steam generators have a continuous flow of water through the system that maintains a solids concentration at acceptable levels in the steam vessel. Additionally, the flow of water controls solids build-up in the steam reactor for direct generators and in the drum or on the tubes for indirect generators. The dissolved solids concentration increases in the steam reactor as more water transitions from liquid to gas as the process moves along. The water with through the most concentrated solids is rejected from the steam generation process to crystallized treatment facilities or disposal wells. Thus, there is a need to eliminate the need for these additional treatment facilities to convert the waste into solid form.
The prior art of down hole direct contact steam generators do not disclose continuous water flow through the system to remove the solids. However, the generated solids are released to a reservoir. These prior art systems are limited to the use of fuels that are clean fuels as well as the need for clean water, since impurities and generated solids can block the reservoir.
There is also a need to utilize low quality carbon fuel such as coal, coke, and asphaltin as the energy source for the steam production in the heavy oil production industry to replace the widespread use of natural gas. Natural gas is a clean and valuable resource that, from a public perspective, should not be used for steam production in heavy oil extraction. This clean resource should be preserved and used for other valuable processes.
There is a major need to produce steam in a thermally efficient way and to inject the generated CO2 back into the reservoir.
There is a need to use low quality water that contains solids like silica clay from tailing ponds, dissolved solids and organic emulsions, like tar and heavy oil based materials. There is now a need that for low quality water to be used directly with minimal additional treatments prior to steam production.
There is a need to extract the continuously produced waste in a dry solid form that can be efficiently and economically disposed of in a landfill.
Above all, there is a need for an apparatus and process that will enable fulfilling the above mentioned needs in a simple and reliable way.
Various patents have issued that are relevant to the present invention. For example, U.S. Pat. No. 2,916,877, issued on Dec. 15, 1959 to Walter, teaches a pressure fluid generator which utilizes direct contact heat transfer. The pressure fluid generator is in the form of an elongated combustion chamber. A coolant in heat exchange relationship is injected into the combustion chamber to form with the combustion products therein as a gas and superheated vapor working mixture at a relatively high temperature and pressure. Some embodiments include in-line soot filters and circulated water, and the fuel is hydrocarbon gas.
U.S. Pat. No. 4,398,604, issued on Aug. 16, 1983 to Krajicek et al. describes a system for above-ground stationary direct contact horizontal steam generation. The method and apparatus produces a high pressure thermal vapor stream of water vapor and combustion gases for recovering heavy viscous petroleum from a subterranean formation. High pressure combustion gases are directed into a partially water-filled vapor generator vessel for producing a high pressure stream of water vapor and combustion gases. The produced solids are continually removed with reject water.
There are also patents related to applications in heavy oil production. U.S. Pat. No. 4,463,803, issued to Wyatt on Aug. 7, 1984 describes a system for down-hole stationary direct contact steam generation for enhanced heavy oil production. The method and apparatus generates high pressure steam within a well bore. The steam vapor generator is constructed for receiving and mixing high pressure water, fuel and oxidant in a down-hole configuration. The produced solids are discharged to the reservoir.
Various patents have disclosed rotational elements in a steam generator. U.S. Pat. No. 1,855,819, issued on Apr. 26, 1932 to Blomquist et al. describes a rotary boiler, where the pressure chamber is rotating inside the combustion area while producing the steam in an indirect heat exchanger. British patent No. 0 328 339, issued on May 1, 1930 to Kalabin teaches a direct contact steam generator with a rotating pressure vessel. The gases flow to a rotating chamber where they are mixed with air and completely burned. Water covers the walls of the rotating chamber by centrifugal force of the rotating chamber, exposing the water to the gas combustion. Russian Patent No. 2 285 199, issued on Dec. 12, 2004 to Krajazhevskikh, describes a steam generator with a rotating chamber with cap-shaped hollow portions. Combustion gases flow between the rotating chamber and a stationary chamber for indirect heat exchange. Japanese Patent No. 581 153 576, issued on Sep. 9, 1983 to Shirou discloses a steam generator with a horizontal rotating heater filled with ceramic balls. Combustion gas is fed to the rotating heater, where the ceramic balls are heated. Solid materials formed into powders or granules are mixed with the heated balls and transferred through a pipe to a stationary boiler. Steam is generated through indirect heat exchange between the pipe and water.
It is an object of the present invention to provide an apparatus and method for the production of high pressure, dry super-headed steam and a combustion gas mixture using direct contact heat transfer between available water and fuel in a rotating reactor.
It is another object of the present invention to provide an apparatus and method where the waste solids generated by combustion and steam generation are driven by gravity to regenerated surfaces at the bottom of the apparatus. These regenerated surfaces are freely rotating spherical bodies that partly fill a rotating vessel of the apparatus. The spherical bodies remove deposits and build-ups of these waste solids.
It is another object of the present invention to provide an apparatus and method where the waste solids are separated and removed from the main flow of the steam and gas mixture without decreasing the steam-gas mixture pressure and temperature.
It is another object of the present invention to provide an apparatus and method that produces steam from low quality tailing pond and reject water containing high levels of dissolved inorganic solids or organic solids, wherein all water is converted to steam and no liquid is discharged from the apparatus.
It is another object of the present invention to provide an apparatus and method that produces steam from low quality fuel containing inorganic impurities like coal, coke, asphaltin or any other available carbon based fuel, wherein the combustion byproducts of this fuel are slag and ash in solid form.
It is another object of the present invention to provide an apparatus and method that minimizes the amount of energy used to produce the mixture of steam and gas that is injected into an underground formation to recover heavy oil.
It is a further object of the present invention to provide an apparatus and method where the low quality water is converted to steam, without any wastewater flow. The concentration of impurities increases to a maximum through the process of a direct contact steam generator, when the impurities can be removed as solid waste.
It is another object of the present invention to provide a process that produces high temperature steam and gas by rotation. Solids are removed in dry form from the hot gas flow. The hot gas flow and the remaining solids are injected into the vessel, where the solids are scrubbed by the water. A saturated wet steam is produced. The slurry of solids and water continue to pass back and recycle through the rotating steam generator. The saturated wet steam-gas mixture is heated by heat exchange with the hot gases leaving the rotating steam generator to produce super-heated dry steam.